<p>Though social connection has been found to be a protective factor against non-suicidal self-injury (NSSI), investigations have primarily focused on the role of social support. This study examined the influence of different facets of social connection on momentary NSSI at both within- and between-person levels.&#xa0;74 participants with past-month suicidal thoughts and behaviors completed 28 days of ecological momentary assessment, reporting on social interactions (duration, valence, meaningfulness), affect, NSSI urges, and NSSI engagement six times per day. Bayesian mixed effects models assessed concurrent and prospective relationships between social connection variables and NSSI.&#xa0;The presence and duration of social interactions did not influence odds of NSSI. Within-person, more positively valenced interactions reduced NSSI odds both concurrently and prospectively, while more meaningful interactions only decreased NSSI odds prospectively. No significant between-person effects were found. Subjective disconnection did not influence odds of NSSI.&#xa0;These findings highlight that momentary fluctuations in the quality, but not necessarily quantity, of social connections influence proximal risk for NSSI engagement. Specifically, they indicate that the mere presence and duration of social interactions is not sufficient to protect against imminent NSSI, rather protective effects are found for positively valenced and subjectively meaningful interactions.</p>